1. Field of Invention
The present invention relates to a production control system and a production control method. More particularly, the present invention relates to a virtual production control system (VPCS), a virtual production control method and a computer program product performing the virtual production control method.
2. Description of Related Art
Under intense global market competition, supply chain management is developed to link the upstream and downstream flows of products, services, and information across businesses to integrate supply and demand. However, supply chains are typically subject to a bullwhip effect, which is caused by cascaded safety stocks for demand forecasts. Notably, the effect spreads to all chain manufacturers when the forecasts are uncertain and time-dependent. Once customer demands are changed promptly, the orders between a manufacturer side and supplier side will be increased or cancelled, thus easily causing the effects of enlarging or shrinking the demands so as to result in the problems of overstocking or understocking. To reduce the bullwhip effect on inventory, a vendor managed inventory (VMI) management model is adopted, wherein the manufacturer shares its material forecast with its supplier and authorizes the supplier to manage and handle the manufacturer side's inventory. The manufacturer shares its internal demand information (material forecast) with the supplier, and the supplier adopts the demand information into its inventory plan so as to determine how many products should be supplied to the manufacturer, thus lowering the bullwhip effect for the overall supply chain. By adopting the VMI management model, the forecast and authorization capabilities may enable the supplier side to produce and delivery material on time and to maintain an agreed inventory of material on the manufacturer side.
The material shortage on the manufacturer side is reduced when the VMI model is used, but the inventory problem is deferred to the supplier side under the unequal relationship with the manufacturer side. Since the manufacturer typically assumes that its supplier owns unlimited capacity to response to the arbitrary material demand changes, which could be caused by factors such as market variation, forecast error, and production variation. To adapt to and tackle these demand changes, the supplier side has to suffer high material inventory for buffering the demand changes using the VMI model. Therefore, the bullwhip effect still exists on the supplier side.
One of the critical factors for the success of supply chain management resides in reality and precision of information sharing, wherein reality refers to the sharing of production progress of the supplier with the manufacturer unmodified, while precision represents the shared information with sufficient time resolution for estimating the material production progress. For instance, in the semiconductor industry, RosettaNet is a popular standard for real and precise WIP information exchanging.
The supplier side's bullwhip effect mainly is resulted from forecast errors and production variations, wherein both factors can be decreased if the shared information, i.e. work in process (WIP) information, is completeness and precision. Additionally, a virtual factory was proposed to serve customers with the corresponding WIP information by demands according to the production estimations in a virtual factory. By using the virtual factory, a customer can ensure its material demand by checking the supplier side's production progress. However, since the virtual factory is located on the supplier side, the supplier side dominates the WIP information which could be modified by the supplier for business concerns. Since the WIP information obtained from the supplier is not sufficient for the manufacturer to change production capacity and material preparation at the supplier side in time, wherein the change of production capacity and material preparation may allow the manufacturer side to response to the possible delay of material delivery, thereby resolving the problems in time and reducing the impact of short-term production fluctuation. It is obvious that modified and inaccurate WIP information eventually induces planning losses and increases production fluctuations on the manufacturer side.
Except for acquiring WIP information, some of suppliers also apply the WIP information to predict their production progress, and to locate their production risks, in which the production parameters from the WIP information are identified to be simulated or programmed according to output schedules. If the production parameters are identified from the modified WIP information, the parameters are definitely fail to support the supplier to estimate and evaluate its production, not to mention the manufacturer needs. Therefore, if the production parameters such as capacity can be identified with the real and precise supplier side's WIP information, and the manufacturer side qualifies the production parameters and brings them into the following demand changes, then the corresponding forecast error and production variation can be decreased, such that the overall inventory in a supply chain can effectively reduced.
Further, a method for making a production control plan to predict production in time beforehand, can only be applied inside a factory at the supplier side, and is described as follows. The factory directly retrieves process or production parameter data from, for example, an internal manufacture system, and then uses a simulation or mathematically planning method to generate a short-term production scheduling plan for the factory itself, thereby preventing production delay and ensuing the customer order-fill rate, thus achieving the objective of short-term production control. Generally speaking, the aforementioned process or production parameter data cannot be directly applied at the manufacturer side to control the supplier side's production, mainly due to business concerns, it is difficult or even impossible for the manufacturer to collect real production situations from the supplier side. Even if the supplier were willing to provide the unmodified production information, the manufacturer also would face the problem of huge data burden. Hence, a typical production control method generally used by a factory to resolve production fluctuation is not suitable in resolving the production fluctuation problem between a manufacturer side and a supplier side in a supply chain.